It depends on the vehicle, setup, and tuning.
My 4-door Explorer sounds better with a little bit of rear fill. I'm driving around right now with the rear speakers off because I am in the middle of changing amps, and it doesn't sound as great as it did before in my particular vehicle. If I had a smaller vehicle, like a car or a two-door truck or SUV, then things would be different. I also use my system for concert DVDs and movies in 5.1, so the rears have a definite role in that. And yes, I carry passengers all the time.
That said, I invested much more into all aspects of the front stage. More power, more tuning, better speakers, etc. And for the majority of people, rears may indeed be a waste of time and counterproductive. Sounds like it in this guy's case. I'd highly suggest dumping more cash into the fronts before even considering the rears, and if you do run rears, send them less power.
My point is that rear fill is not always a waste.